1. Field of the Invention
The present invention relates to a telecentric lens system and an image measuring device.
2. Description of Related Art
What is called a double telecentric lens system is known. The double telecentric lens system comprises two lens units, a front lens unit and a rear lens unit, with the back focal point of the front lens unit and the front focal point of the rear lens unit being disposed so that they coincide, and a diaphragm disposed at the location where these two focal points coincide.
In the double telecentric lens system, the field of view of an object is wide, the focal depth is large, and the imaging magnification is determined by the focal lengths of the front lens unit and the rear lens unit regardless of the position of the object. Therefore, the telecentric lens system is frequently used to observe objects having stepped portions, such as edge tools, mechanical parts, and assembled electronic parts.
However, in the telecentric lens system, in principle, the resolution and the focal depth are inversely proportional to each other. In other words, when the focal depth is increased, the resolution is reduced. In order to observe an object with higher resolution after setting a large focal depth once, it is necessary to either change the lens being used to one having a higher magnification or separately observe an object with a microscope having high resolution. Changing lenses and separately using a microscope make it more troublesome to observe an object, thereby making the operation for observing the object complicated, so that operation efficiency is reduced. In addition, separately providing a lens or a microscope is costly.
Accordingly, it is an object of the present invention to overcome the aforementioned related problems, and to provide a telecentric lens system that can be used in observations for a wide range of applications and an image measuring device.
To this end, according to one aspect of the present invention, there is provided a telecentric lens system comprising a front lens unit; a rear lens unit that is disposed so that the front focal point of the rear lens unit coincides with the back focal point of the front lens unit; and a diaphragm mechanism that is disposed at the location where the back focal point of the front lens unit and the front focal point of the rear lens unit coincide, and which comprises a numerical aperture changer for changing the numerical aperture of the diaphragm mechanism.
According to such a structure, since the diaphragm mechanism comprises a numerical aperture changer, the numerical aperture can be changed. In the telecentric lens system, the focal depth and the resolution are inversely proportional to each other. When the numerical aperture is reduced by the numerical aperture changer, the resolution is low, but the focal depth is large. In other words, an object having a stepped portion can be observed clearly and measured. On the other hand, when the numerical aperture is increased by the numerical aperture changer, the focal depth becomes small, but the resolution is high. In other words, an object can be observed and measured with precision and high resolution.
By changing the numerical aperture by the numerical aperture changer, the telecentric lens system can be used in a wide range of applications from those requiring a large focal depth to those requiring high resolution. Therefore, one telecentric lens system can be successively used for observations for different applications. As a result, operation efficiency is remarkably increased. In addition, since it is not necessary to separately provide, for example, a microscope according to the type of application, costs can be reduced.
In a first form based on the one aspect, the numerical aperture changer has at least two diaphragms having numerical apertures that differ successively, and, by changing one diaphragm with another diaphragm, the numerical aperture is changed.
According to such a structure, the numerical aperture can be changed by changing a diaphragm with one having a different numerical aperture. Therefore, one telecentric lens system can be successively used for observations for different applications (such as, applications requiring large focal depths or high resolution). As a result, operation efficiency can be increased. In addition, since it is not necessary to separately provide a microscope, costs can be reduced.
If a plurality of diaphragms having previously specified numerical apertures are provided and optical features (such as focal depth and resolution) in terms of the numerical apertures of the respective diaphragms are known, optimal numerical apertures can be easily selected according to various objects to be observed and various applications. Since the optical features are known when, for example, an observed image is processed and measured, the image can be optimally measured.
In a second form based on the first form, the diaphragms are successively provided in one plate, and, by moving the plate, the numerical aperture is changed.
The diaphragms may be provided in one row in one plate or along the circumference of one plate. According to such a structure, the numerical aperture can be changed by moving the plate. Therefore, the structure is simple, and observations for different applications can be successively carried out using one telecentric lens system by only simply moving the plate, so that operation efficiency can be increased.
In a third form based on the first form, the diaphragms are provided in swingably supported levers, respectively, and, by movement of any one of the levers, the numerical aperture is changed.
It is desirable that the levers are provided perpendicular to the optical axis and be supported so that they swing within a plane that is perpendicular to the optical axis. In addition, it is desirable that the levers having different numerical apertures be disposed along the optical axis.
According to such a structure, if a lever having the desired numerical aperture is moved, so that the diaphragm is disposed on the optical axis, the numerical aperture is changed. By selecting the numerical aperture according to the object to be observed and the type of application, observations for different applications can be successively carried out using one telecentric lens system, so that operation efficiency can be increased.
In a fourth form based on the one aspect, the numerical aperture changer comprises an iris diaphragm for successively changing the numerical aperture.
According to such a structure, by adjusting the shutter of the iris diaphragm, the numerical aperture can be successively changed. Since the numerical aperture can be successively changed, the numerical aperture can be adjusted to an optimal numerical aperture according to the type of application. Therefore, observations for different applications, such as an observation requiring a large focal depth or that requiring a high resolution, can be successively carried out using one telecentric lens system. As a result, operation efficiency can be increased. Since it is not necessary to separately provide a microscope according to the type of application, costs can be reduced.
In a fifth form based on the one aspect to the fourth form, either the front lens unit or the rear lens unit is changeable.
According to such a structure, by the numerical aperture changer, observations ranging from those requiring a large focal depth to those required high resolution can be carried out. In addition, by changing lens units, the setting range of focal depths and the setting range of resolutions can be increased. Conventionally, when a numerical aperture changer is not provided, the focal depth and the resolution are uniquely determined for one lens unit. Therefore, in order to provide a wide range of focal depths and resolutions, it is necessary to provide a large number of lens units. However, in the present invention, by the numerical aperture changer, the setting range of focal lengths and the setting range of resolutions of one lens unit can be increased, so that the number of lens units that are provided can be reduced. Therefore, it is possible to reduce costs for carrying out observations and measurements for a wide range of focal lengths and resolutions.
According to another aspect of the present invention, there is provided an image measuring device comprising the telecentric lens system of any one of the one aspect to the fifth form, and an imaging optical system that is connected to the telecentric lens system.
According to such a structure, an image measuring device that provides the advantages of the telecentric lens systems of the one aspect to the fifth forms can be provided. In other words, observations for different applications can be successively carried out using one image measuring device. As a result, operation efficiency is remarkably increased. In addition, since it is not necessary to separately provide an image measuring device according to the type of application, costs can be reduced.